The present invention generally relates to metal cutting machine tools and, more particularly, a device for protecting the spindle headstock of a machine tool in the case of an accidental collision with a workpiece.
As known, in recent years manufacturers in the field of machine tools have directed their efforts to improve, in addition to the quality of machining, also the efficiency of machine tools by gradually and continuously reducing machine time and machine setup time.
At present, machine time has become reduced thanks to the improvements in the quality of the cutting edges of tools and, in particular, to their wear resistance, and also has become reduced because the cutting speed has increased.
Machine tool manufacturers are now endeavored to reduce, in the work cycle, the machine tool setup time which relates to retooling operations, workpiece loading and unloading operations, workpiece dimensional check operations and, not in the least, positioning operations of the spindle headstock in required various machining configurations.
It can be clearly understood that a reduction of the machine tool setup time is especially important in the case of a 24-hour work cycle, wherein a few minutes lost in the machine tool setup operation during the production of a workpiece, once they are multiplied by the daily production, can result in the loss of several hours.
Since each hour lost in the machine tool setup operation has a negative effect on the returns the invested capital must yield, the importance of reducing the machine tool setup time to a minimum is clearly understood.
For this reason, the current tendency of machine tool manufacturers is to use movable spindle headstocks having very high feed speeds. In particular, the time required for positioning the spindle headstock has been greatly reduced by increasing the feed speed of the spindle headstock to a top limit of 80 m/min by using improved drives.
On the one hand, the increase in the feed speed of the spindle headstock permits a great amount of machine tool setup time to be saved, but on the other hand it exposes the spindle headstock to the risk of colliding with the workpiece as a result of a wrong control, an excessive delay of the response to a control or an inaccurate positioning.
It must be taken in account that because of the inertia and speed involved, in the event of a collision, forces of great intensity would be developed and the resulting decrease of kinetic energy would be converted into internal energy which would be absorbed and dissipated in the workpiece and the spindle headstock, thus causing great damage to both and especially to the latter.
Therefore, any damage to the spindle headstock resulting from a collision with the workpiece must be absolutely avoided because the spindle headstock is easily damaged and accurately designed, and thus an expensive part of the machine tool.
The present invention is intended to reduce to a minimum the damage to a spindle headstock caused by an accidental collision with a workpiece during the positioning in an operative work configuration by providing a shock-absorbing device for the spindle headstock.
More particularly, the shock-absorbing device is intended to be mounted on the spindle headstock of a machine tool. The spindle headstock includes a motor driven spindle unit connected to an upright by a support. The spindle headstock comprises a yieldable structure connected on one side to the spindle unit and on the other side to the support, and is adapted to yield upon an accidental collision of the spindle headstock with a workpiece. A collision sensor is associated with the yieldable structure for detecting the yielding thereof resulting from an accidental collision of the spindle headstock with the workpiece, and for transmitting in response thereto a signal to a machine tool control unit.